In recent years, active studies have been made to develop devices having novel functions, such as a field effect transistor (MOSFET) in which ferromagnetic layers or stacked structures formed with ferromagnetic layers and tunnel barrier layers (ferromagnetic layer/tunnel barrier layer) are provided as ferromagnetic electrodes on the source region and the drain region (hereinafter also referred to as the source/drain regions). One of those devices is a spin MOSFET in which the source/drain regions contain a magnetic material. Such a spin MOSFET is characterized in that the output characteristics can be controlled simply by switching the spin moment direction of the magnetic material in the source/drain regions. With such spin MOSFETs, it is possible to form a spin MOSFET structure or a reconfigurable logic circuit that has a reconfigurable function and an amplifying function.
As a method of writing to switch spins, a method of writing using a spin transfer torque technique has been suggested. Spin switching caused in a magnetic material by flowing spin-polarized current into the magnetic material have been observed. To use spin transfer torque writing in spin MOSFETs, there has been a suggested structure in which a MTJ (Magnetic Tunnel Junction) is provided on at least one of the source and the drain.
As a method of orienting a tunnel barrier layer, formation of an amorphous underlayer between a semiconductor layer and the tunnel barrier layer has been suggested. However, the use of an amorphous underlayer reduces the effect to achieve a low interfacial resistance.